The present invention relates generally to resilient rear wheel suspension systems, and more particularly to a leverage assembly attached to the rear shocks and frame of a standard motorcycle to increase the maximum vertical travel of the rear wheel and provide progressive resistance to rear wheel vertical travel caused by loading of the suspension.
In motocross or other rough terrain riding, the rear suspension system of a standard motorcycle is generally modified to increase the maximum vertical travel of the rear wheel. This is done to minimize the motorcycle "bottoming out" under extreme loading. In a standard, stock motorcycle, each rear shock absorber, which is generally an air or oil cooled adjustable unit, is pivotally connected to the motorcycle frame just below the seat at one end, and to the swing arm slightly forward of the rear wheel axle at the other end. This arrangement typically provides approximately 3 or 4 inches of maximum vertical travel or "arc" of the rear wheel. Although this is adequate for road riding or even light scrambling, 7-10 inches is necessary for motocross riding, particularly for competition.
In the past, the standard techniques for increasing the maximum vertical travel of the rear wheel have been to (1) move the lower end of each shock absorber forward of the standard lower shock mounts on the swing arms, (2) move the upper end of each shock absorber forward of the standard upper shock mounts or (3) move both the upper and lower ends of each shock absorber forward of the standard upper and lower shock mounts.
While generally somewhat satisfactory, these three techniques require substantial technical expertise because the rear suspension of a motorcycle significantly affects handling and is critical for competition riding. In addition, these techniques require cutting or welding the frame and are impracticable for the novice rider.
Moving either the lower or upper end of each shock absorber forward of the standard shock mount, known as the angled shock techniques (techniques 1 and 2), causes the rear wheel suspension system to exhibit a regressive resistance characteristic, i.e., becomes softer with loading of the suspension. This is because the shocks divert from their normal (stock) orientation with respect to the arc described by the rear wheel with loading and thus provide a resistance to rear wheel loading that decreases as the wheel approaches the top of its travel. This characteristic encourages an undesirable "bottoming out" of the motorcycle.
In order to compensate for regressive rear wheel resistance in angled shock suspensions, enduro motorcycles utilize spring-type shock absorbers that are extra heavy-duty, but extra heavy-duty shocks cause the suspension to be too stiff when the suspension is lightly loaded. A progressive spring shock absorber is used in some enduro motorcycles to partially offset the regressive resistance characteristic of the suspension. The progressive shock has a non-linear helical spring which provides a resistance to wheel travel that increases as the spring is compressed, i.e., becomes stiffer with loading of the suspension. Although the progressive shock partially offsets the inherent regressive resistance characteristic of the angled shock techniques, compensation is incomplete especially in the long travel rear wheel suspensions used for competition riding.
The technique of moving both the upper and lower ends of each shock forward of the standard upper and lower shock mounts (technique 3) provides a constant resistance characteristic to vertical rear wheel travel. The constant resistance characteristic is unsuitable for motocross riding using this arrangement because the shocks are unable to handle the increased moment of inertia of the rear wheel with respect to the shocks caused by the increased distance between the rear wheel axle and the shocks.
A somewhat increased moment of inertia of the rear wheel with respect to the shocks also exists in the aforementioned angled shock techniques, due to the increased distance between the shocks and rear wheel, whereby the shocks are more heavily loaded during riding and tend to overheat and fail at an excessive rate. In all three techniques the increased moment of inertia of the rear wheel creates increased stress on the frame of the motorcycle and the frame requires reinforcement.
Accordingly, one object of the present invention is to provide a new and improved rear wheel suspension for a motorcycle.
Another object of the present invention is to provide a motorcycle suspension system having increased maximum rear wheel vertical travel.
Another object of the present invention is to provide a rear wheel suspension system for a motorcycle which provides progressive resistance to rear wheel vertical travel.
Another object of the present invention is to provide a heavy-duty rear wheel suspension system that is attachable to a standard motorcycle without requiring special tools or technical expertise.
Another object of the present invention is to provide a new and improved rear wheel suspension system for a motorcycle which permits heavy-duty riding, such as motocross, without requiring extra heavy-duty shocks.
Another object of the present invention is to provide a rear wheel suspension system for a motorcycle which permits heavy-duty riding, such as motocross, without substantially increasing stress on the frame.